Electrical control system



May-17, 1949. E, ND 2,470,119

ELECTRICAL CONTROL SYSTEM Filed Dec. 15, 1944 INVENTOR.

Patented May l7, 1949 2,470,119 ELEGTRIGAL; (SON'DROL SYSTEM Gustav E. Uhdy; Detroit, Mich., assignor to Wel troni'cGomp'any; Detroit,- Mich, a corporation at' Michigan Application" December-'15, 1944, Serial No. 568,317

(Cl.-3l5201) 13 Claims. 1;

Thepresent inventiomrel-ateslto electrical: con-.- trol systems and; is-.particularly directedxto the provision of improved. andsimplified meansfor. effecting thestarting of mercury; arc rectifiers of these-called mercury; pool immersed igniter type.

Principal objects of the present invention .areto provide a systemofthe-aforesaid type which is simplex-inarrangement andvwhi-ch is reliable and efficient in operationytdprovide such a system wherein the initiation of: aldischarge between the electrodes of latrectifier, servesto substantially ifvnot: entirely eliminate the-.flow of current to the igniter electrode: of. thevrectifier; and to generally improve. and. simplify I thearrangement of systems-of the aforesaidxtype;

With theabove as well asother and more dee tailed objects in view, which appear in the following. description. and in-=thea pended claims, a preferredbutillustrative embodiment of the in? vention:- is shown lathe-accompanying drawing in.which the sole figure is-a-diagrammatic View otacontrol system for a resistance welder, embodying theinvention.

It willbejappreciated from a complete understanding of the present invention, that .in a generic sense, the improvements thereof may be em-- bodied. incontroL systems.v designed for widely diifering applications, and suchv control systems, and therectifiers controlled thereby may them-. selves beofwidelydifferingconstructions and arnangements.

In the drawing, a pair of usual mercury arc rectifiers Inland lzareconnectedin anti-parallel relation, to control thefiow of'current from an alt'ernating current. source L|--L2, to an illustrative load L. Load. LI is'illustrated as being a usual resistance welding circuit,. the work-engaging. electrodes l4-l6'whereof are connected in a local. circuit with the secondary winding of a usual welding transformer.

Rectifiers.l'l2are illustrated as being of the conventional'mercury pool immersed igniter type,

tiated,.the igniter loses control; .and'the discharge.

continues solongastheabovevdescribed"discharge;

2: sustaining. potential is maintained between the anode and the cathode;-

In accordance'with the present inventiomr'ecti fiers l0 and mare-provided with identical-firing circuits. More particularly, the ignit'eri of reo'ti--= fier lfll-is connected tothe cathode'througha circuit which includes in: ser-iesea usualunidirec tional conductor l8' and'atheseconda'ry winding- 20 ofa control transformeriCT; The igniter circuit for rectifier I2 includesl corresponding elements 22- and 24 The primary winding-.26. ofijcontrol transformer CT is connected across 'the'anod'esof-v rectifiers I Band: 12 ,rinseries'with a control 1 device 28 which is herein illustrated as being a manually operable pilot switch;

As to". operation, .it:will'-:be appreciated that so long as line conductors 'Ll' and-LI are'renergized; thez line voltage is; impressedxacross the anodecathode circuit of each rectifier "land-12. Normally, being monoonductive; these: rectifiers serve. as a circuit breaker: w'hichiprevents: flow of current to the load.

In order toinitiate a-fiow'of current to-the load, switch 28 maybe closed; which-operation forpresent purposes, may beassumed to take place atrandom relative to the periodicity-of thesourcev Assuming that conductor LI is positive at the time switch 28 isclosed, it will be appreciated that-such closure initiates a flow, of current-through winding 26,. in a direction which causes the induced voltage in winding .211v to render its associated. igniteri positive with respect tothe corresponding cathode c. Rectifier. I8 is poledtopermit aflow of: current under. these conditions and in conse--- quence thereof an igniting; current-flows between the igniter i andfits cathode c. This-flow of cur-- rent .initiates a discharge between the anode and.- the cathode of rectifier I01 As soon as this maindischarge is initiated; the potential difference between line .conductorLl and terminal 30 fallsto. a, comparatively low value,- equalonly to the. arc dropthrough rectifier Iii Rectifier liilthus; serves tovirtuallyshort circuit-transformer windmg 26; causing the. induced secondary voltage;

.thereof to .fall' to aecorrespondingly low value.

Under the aforesaid .starting. conditions, the voltage induced in secondary winding ZA-tends to cause current flow in a direction in which rectiher 22 isnon-conductive. Substantially no: cur- .rent. whatsoever therefore passes through the igniter circuit of I rectifier I2 under conditions whenrectifier I0 is-to befiredr At the conclusionof thehalf cycle of currentfiow through rectifierv lll'g -the discharg there through, is extinguishedv At. the instant that-this"- discharge is extinguished, the voltage across transformer winding 26 again rises to an effective value. At the time conductor Ll is negative with respect to conductor L2, consequently the induced voltage in transformer winding 24 is of the proper polarity to cause a flow of firing current through the igniter circuit of rectifier i2, such current in the firing circuit of rectifier I being blocked by rectifier [8. The flow of firing current in the firing circuit of rectifier i2 initiates a discharge therethrough, again virtually short circuiting winding 26 and interrupting further flow of any substantial amount of current in the associated firing circuit.

So long, therefore, as switch 28 remains closed, rectifiers l0 and I2 are alternately rendered conductive. If switch 28 is opened, such action has no immediate efiect upon the flow of load current during the half cycle then in progress. Such load current is interrupted when the then active rectifier is extinguished, at the conclusion of such half cycle. In view of the now open condition of switch 28, no flow of load current is initiated through the companion rectifier at the beginning of the following half cycle.

It will be appreciated that in practice transformer CT is arranged so that the secondary outputs are of sufiicient magnitude to insure prompt firing of the associated main rectifiers, under the aforesaid conditions. At the same time transformer CT is so proportioned that the secondary outputs, when either main rectifier is conductive, are so low as to have no adverse effect on the igniters i.

It will further be appreciated that switch 28 may be subjected either to manual or automatic control and that it may be regarded as representing, for example, an electrically or mechanically operated element which closes and opens in synchronizing relation to the source LI--L2.

Although only a single specific embodiment of the invention has been described in detail, it will be appreciated that various modifications in the form, number, and arrangement of the parts may be made Without departing from the spirit and scope of the invention.

What is claimed is:

1. In a control system for an electric valve of the immersed igniter mercury pool type, having principal electrodes, and disposed to abruptly change from a non-conductive to a conductive condition in response to the application of a critical potential to said igniter for controlling the flow of current between a source of supply and a load, the combination of an electrical translating device adapted to supply said critical potential, means including unidirectionally conductive means for coupling said translating device between said igniter and one of said principal electrodes, control means for controlling the energization of said translating device and having a first control position in which said translating device is enabled to supply said critical potential, and means responsive to a conductive condition of said valve for reducing the energization of said translating device to a potential not in excess of the potential between said principal electrodes.

2. The combination of claim 1 wherein said translating device is a transformer, having its secondary winding coupled between said igniter and said one principal electrode, and having its primary winding connected in parallel with the principal electrodes of the valve whereby the potential impressed on said primary winding is the same as the potential across the principal electrodes.

3. The combination of claim 1 wherein said translating device is a transformer, having its secondary winding coupled between said igniter and said one principal electrode, and having its primary winding connected in parallel with the principal electrodes of the valve whereby the potential impressed on said primary winding is the same as the potential across the principal electrodes, and said control means is selectively operable for controlling said connection for said primary winding.

4. In a control system for controlling the flow of current from an alternating current source to a load, a pair of reversely connected discontinuous control-type electric valves each having principal electrodes and a control electrode, a transformer having a primary winding connected between one of said principal electrodes of each of said valves and having a pair of secondary windings, means adapted to connect the principal electrodes of each of said valves in series circuit between the load and the source, and means connecting each secondary winding between the control electrode and the other of said principal electrodes of the corresponding valve.

5. The combination of claim 4 wherein each said secondary connection includes unidirectionally conductive means.

6. The combination of claim 4 including selectively operable control means for controlling the energization of said primary winding.

7. In an electrical network for controlling the flow of alternating current from a source to a load, a pair of mercury pool-type electric valves, each said valve having an anode and a cathode and an igniter, means adapted to be connected to the source and electrically interconnecting said anode of one of said valves with said cathode of the other of said valves, means adapted to be connected to the load and electrically interconnecting said anode of said'other valve with said cathode of said one valve, a transformer havin a primary winding and a pair of secondary windings, means connecting said primary winding di rectly across said anodes, means connecting one of said secondary windings between said igniter and said cathode of said one valve, and means connecting the other of said secondary windings between said igniter and said cathode of said other valve.

8. In an electrical network for controlling the flow of alternating current from a source to a load, a pair of mercury pool-type electric valves, each said valve having an anode and a cathode and an igniter, means adapted to be connected to the source and electrically interconnecting said anode of one of said valves with said cathode of the other of said valves, means adapted to be connected to the load and electrically interconnecting said anode of said other valve with said cathode of said one valve, a transformer having a primary winding and a pair of secondary windings, means connecting said primary Winding directly across said anodes, means connecting one of said secondary windings between said igniter and said cathode of said one valve, means connecting the other of said secondary windings between said igniter and said cathode of said other valve, and

switch means for controlling the energization of said primary winding.

9. In an electrical network for controlling the flow of alternating current from a source to a load, a pair of mercury pool-type electric valves,

each said valve having an anode and a cathode and an igniter, means adapted to be connected to the source and electrically interconnecting said anode of one of said valves with said cathode of the other of said valves, means adapted to be connected to the load and electrically interconnesting said anode of said other valve with said cathode of said one valve, a transformer having a primary winding and a pair of secondary windings, means connecting said primary winding directly across said anodes, means connecting one of said secondary windings between said igniter and said cathode of said one valve, means connecting the other of said secondary windings between said igniter and said cathode of said other valve, and unidirectional current conducting means interposed in each of said secondary connecting means whereby current can flow solely from said igniters to said cathodes, each of said secondary windings being so phased relative to its respective one of said valves to provide current flow when said anode of said respective valve is positive relative to its cathode.

10. In an electrical network for controlling the flow of alternating current from a source to a load, a pair of mercury pool-type electric valves, each said valve having an anode and a cathode and an igniter, means adapted to be connected to the source and electrically interconnecting said anode of one of said valves with said cathode of the other of said valves, means adapted to be connected to the load and electrically interconnecting said anode of said other valve with said cathode of said one valve, a transformer having a primary winding and a pair of secondary windings, means connecting said primary winding directly across said anodes, means connecting one of said secondary windings between said igniter and said cathode of said one valve, means connecting the other of said secondary windings between said igniter and said cathode of said other valve, unidirectional current conducting means interposed in each of said secondary connecting means whereby current can flow solely from said igniters to said cathodes, each of said secondary windings being so phased relative to its respective one of said valves to provide current flow when said anode of said respective valve is positive relative to its cathode, and switch means for controlling the energization of said transformer.

11. In a control system for an electric valve of the immersed igniter mercury pool type having principal electrodes and disposed to abruptly change from a nonconductive to a conductive condition in response to the application of a critical potential to said igniter for controlling the flow of a current between a source of supply and a load, the combination of an electrical transformer having a primary and a secondary winding and adapted to supply said critical potential, circuit means including unidirectional conductive means for coupling said secondary winding between said igniter and one of said principal electrodes, control means for controlling the energization of said transformer and having a first control position in which said transformer is enabled to supply said critical potential, and means responsive to a conductive condition of said valve for reducing the output potential of said secondary winding to a potential not in excess of the potential between said principal electrodes.

12. The combination of claim 11 in which said unidirectional means permits flow of substantial current solely in a direction toward said igniter from said secondary winding.

13. In a control system for controlling the flow of current from an alternating source to a load, a pair of reversedly connected electric valves of the immersed igniter mercury pool type each having principal electrodes and disposed to abruptly change from a nonconductive to a conductive condition in response to the application of a critical potential to said igniter for controlling the fiow of current therethrough, a transformer having a primary winding with its terminals connected between corresponding ones of said principal electrodes of each of said valves and having a pair of secondary windings, circuit means adapted to connect the principal electrodes of each of said valves in series circuit between the load and the source, and circuit means including a unidirectional current flow device for connecting respective ones of said secondary windings between the respective said igniters and the other of said principal electrodes of corresponding valves, said flow devices permitting substantial current to flow only in a direction from said secondary windings to said igniters.

GUSTAV E. UNDY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,069,283 Slepian Feb. 2, 1937 2,261,144 Dawson Nov. 4, 1941 2,342,673 Klemperer Feb. 29, 1944 2,366,561 Schmidt Jan. 2, 1945 OTHER REFERENCES Gulliksen 8: Vedder: Industrial Electronics, 1935, John Wiley 8: Sons, N.Y.C., pp. to 134 (copy in Div. 54). 

